This invention generally relates to medical devices, and particularly to catheters for angioplasty and stent delivery.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient""s coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairng or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion.
Typically, the distal section of a balloon catheter or other percutaneous device will have a radiopaque marker which the operator of the device can see under x-ray or fluoroscopy imaging. Generally, a band or ring of solid radiopaque metal is secured about an inner or outer shaft of a balloon catheter to serve as a radiopaque marker. Such a configuration may add stiffness and discontinuity to the catheter shaft as the solid metal bands are relatively inflexible compared to a polymeric balloon catheter shaft. There are several methods for adhering radiopaque metal materials to a catheter component. However, processes which expose polymeric catheter components to relatively high temperatures may melt or otherwise adversely affect the performance characteristics of the component. What has been needed is a radiopaque marker for intracorporeal devices with improved performance characteristics.
The invention is directed to a catheter having a radiopaque marker, and a method of making a radiopaque marker on a catheter component in which an outer layer of radiopaque material is electroplated onto an inner layer of radiopaque material. In one embodiment of the invention, a catheter component has a radiopaque marker having a first layer of radiopaque material, and a second layer of radiopaque material on the first layer with a thickness greater than the thickness of the first layer. In one embodiment of the invention, a radiopaque marker has a first layer of radiopaque material formed of a blend of polymeric material and radiopaque material, and a second layer of radiopaque material electroplated onto the blended first layer. A method of making a radiopaque marker on a catheter component generally involves depositing a first layer of radiopaque material onto at least a section of the catheter component, which in a presently preferred embodiment is deposited by thin film deposition, and electroplating a second layer of radiopaque material onto an outer surface of the first layer of radiopaque material. In one embodiment, the catheter component having the radiopaque marker is a balloon on a balloon catheter. However, the radiopaque marker of the invention may be on a variety of catheter components including a catheter shaft.
In one embodiment, the first layer of radiopaque material is applied by a thin film deposition technique, such as chemical vapor deposition (CVD), or physical vapor deposition (PVD). Specifically, PVD methods useful in the method of the invention include sputtering, and ion beam assisted deposition (IBAD) which is a vacuum deposition process combining PVD and ion beam bombardment available from Spire Corporation. In CVD, a chemical reaction in the vapor phase of a gas stream produces a compound which is deposited downstream onto a substrate. In PVD, energy applied to a target removes material from the target as a vapor which is deposited onto a substrate. A presently preferred method of applying the first layer of radiopaque material involves sputtering, in which a target formed of the radiopaque material is bombarded with energetic electrons and the resulting vaporized material is deposited onto the surface of the catheter component.
The radiopaque marker must be sufficiently thick to provide adequate radiopacity under fluoroscopy. During thin film deposition of radiopaque material, thicker layers of deposited radiopaque material formed using longer processing times result in the catheter component being exposed to higher temperatures. One embodiment of the invention minimizes or avoids damage to the catheter component caused by exposure to high temperatures by minimizing the thickness of the first layer applied by thin film deposition, and electroplating a second layer of radiopaque material onto the first layer.
The first layer of radiopaque material is deposited onto the catheter component in a sufficiently short period of time to avoid adversely and excessively heating the catheter component. However, the first layer of radiopaque material has sufficient conductivity to allow the second layer of radiopaque material to be electroplated onto the first layer. Additionally, the first layer of radiopaque material is sufficiently thick to substantially lower the process time required to complete the radiopaque marker by electroplating the second layer. In one embodiment of the invention, the first layer and second layers of radiopaque material are selectively applied to the catheter component, i.e., the layers have a length less than the length of the catheter component. In one embodiment, the radiopaque markers have a length substantially less than the length of the catheter component. In the embodiment in which the catheter component is a balloon, the radiopaque marker having a length substantially less than the balloon length has a length not more than about 2% to about 10%, preferably about 2% to about 5% of the balloon length. In the embodiment in which the catheter component is a catheter shaft, the radiopaque marker having a length substantially less than the shaft length has a length not more than about 0.005% to about 0.05%, preferably about 0.006% to about 0.04% of the shaft length. A mask may be used on portions of the catheter component, so that only a desired section of the component is exposed during the thin film deposition of the first layer.
Variables such as the radiopaque material type, particle size, and layer thickness may be varied to improve adhesion of the radiopaque material layers. The radiopaque material used to form the first layer may be the same as or different from the radiopaque material forming the second layer, and a variety of suitable radiopaque materials may be used, including gold, tungsten, and platinum/iridium alloys. Any metal ions can be used as the first layer, to provide a substrate which attracts the radiopaque material of the second layer during the electroplating process used to form the second layer, but are preferably a highly radiopaque material. The radiopaque materials are preferably easily deposited and relatively soft. A presently preferred material for the first and second layer is gold. The first and second layers may be formed of materials having different particle sizes.
Any number of radiopaque markers of the invention can be secured to a component of the catheter, such as the catheter balloon or catheter shaft, having the same or varied configurations. In embodiments of the invention where a plurality of radiopaque markers are secured to the catheter, the markers may be spaced at regular intervals in order to provide a measuring function. Additionally, the markers may provide a visualization function by marking features of interest of the balloon catheter, such as proximal and distal ends of the balloon, rapid exchange ports, or a distal extremity of the catheter. In a presently preferred embodiment, the markers are applied to the proximal and distal ends of the working length of a balloon which has been formed by blow molding. In one embodiment, the radiopaque marker of the invention is provided on a shaft inner tubular member when, for example, possible damage to the patient""s vessel from a marker located on an outer surface of the catheter could occur.
The radiopaque markers of the invention applied to a surface of a balloon are particularly useful in balloon catheters having an opaque balloon. Specifically, during assembly of the catheter, radiopaque markers on the inner tubular member must be correctly aligned at either end of the balloon working length. This procedure is complicated by the opaque balloon which obscures the view of the markers. Additionally, a catheter inner tubular member which is present only to provide a place for the radiopaque markers can be eliminated where the radiopaque markers of the invention are applied to a surface of the balloon.
The method of the invention avoids damage to the catheter component caused by exposure to high temperatures, due to the first layer of radiopaque material applied by thin film deposition and the second layer of radiopaque material applied by electroplating. As a result, unreasonably long process cycle times required to apply a thick radiopaque marker solely by thin film deposition are avoided. Moreover, the radiopaque markers of the invention can be applied to a surface of the balloon without damaging the balloon, despite the thinness of the balloon wall and the need for strictly controlled balloon dimensions. Additionally, the radiopaque markers of the invention may be made thinner than conventional marker bands which are formed of a machined metal ring. Machined metal ring markers have a thickness lower limit equal to the minimum wall thickness required to draw the metal tubing that forms the conventional marker bands, which is not required in the radiopaque markers of the invention.
These and other advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying exemplary drawings.